Tiangong 2

China’s second Space Laboratory module, designed to demonstrate the medium-term orbital living and on-orbit refuelling capabilities, as well as to carry out space science and applications experiments. Launched in September 2016 and visited by the Shenzhou 11 and Tianzhou 1 missions.

Programme

History

Five years after the launch of the first Space Laboratory module Tiangong 1, the China Manned Space Programme (CMSP) was ready to launch a second module. Two identical modules were originally built for the Tiangong 1 mission. After the successful launch of Tiangong 1, its backup was modified into an improved module added with upgraded systems and new capabilities, most notably the ability to be resupplied and refuelled by a Tianzhou cargo vehicle.

To ensure the ‘new’ space module was still qualified for orbital flight after spending five years inside the spacecraft hangar at CAST, engineers had to carefully assess the conditions of nearly 300 components and parts on the module, either putting them through a life-extension process or replacing those that no longer met the requirements.

Unlike its predecessor Tiangong 1, which was mainly intended as a target vehicle for perfecting orbital rendezvous docking, Tiangong 2’s main objective was to “verify key technologies including cargo transportation, on-orbit propellant resupply, and medium-term stay of astronauts”, as well as “conducting space science and application experiments on a relatively large scale”, according to the programme’s official statement.

In February 2016, Chinese state media cited sources from the China Manned Space Agency (CMSA) that the country would orbit its second space laboratory Tiangong 2 in third quarter of this year, followed by a single expedition mission Shenzhou 11 in the fourth quarter of the same year and an experimental cargo resupply mission Tianzhou 1 in the first half of 2017.

Launch Campaign

The launch campaign began with the arrival of the Tiangong 2 module at the launch centre on 9 July, after a two-day train journey from its fabrication facility at the Beijing Space City. Upon its approval, the Tiangong 2 module was examined and assembled inside the Spacecraft Non-Hazard Operation Building, before being moved to the Spacecraft Hazard Operation Building for the irreversible process of fuelling with liquid propellants and loading of pressurised gases. The completed spacecraft inside its payload fairing was rolled to the Launch Vehicle Vertical Processing Building, where the CZ-2F launch vehicle was assembled. The spacecraft inside the payload fairing was then hoisted onto the top of the launch vehicle for payload integration.

On 9 September, the CZ-2F/Tiangong 2 launch vehicle stack sitting vertically atop the Mobile Launcher Platform (MLP) was rolled out to Pad 921 situated 1.5 km away from the processing building. Once the launch vehicle stack arrived at the pad, the rotating platforms of the umbilical tower were swung to ‘embrace’ the vehicle to allow the final checkout procedure to be conducted. After the mission managers gave a Go to the launch, fuelling of the CZ-2F launch vehicle with liquid propellants began in the morning of 14 September.

The CZ-2F (T2) launch vehicle, which lifted off from Jiuquan at 22:04 CST on 15 September, inserted the Tiangong 2 module into an initial 350 x 200 km parking orbit with an inclination of 42°. The next day, the space module used its own propulsions to make two orbit elevation manoeuvres, moving onto a 380 km near-circular orbit. Over the next few weeks, the ground mission control carried out various checks remotely to ensure that the space module is readied for the docking operation.

Spacecraft Design

General Design

The Tiangong 2 module is almost identical to its predecessor in size and appearance, consisting of two cylinder-shaped sections: a habitable Experiment Compartment serving as the main living quarters and laboratory for the crew; and an inhabitable Service Compartment that houses propulsion, power, life support, and communications systems. A pair of solar wings each with 4 solar panels are attached to the Service Compartment. The space module is 10.4 m in length and 3.35 m in diameter, with an orbital mass of 8.6 t.

The front Experiment Compartment is 5 m in length and 3.35 m in diameter, with a habitable internal volume of 14.4 cubic metres (2.0 x 1.8 x 4.0 m). The front end of the compartment, which provides a small free space for the crew to live and conduct experiment, is surrounded by heat pipes designed to conduct heat from internal systems to an external radiator. Inside the compartment is an instrument panel for flight controls and communications, a foldable table for eating and conducting experiments, and two sleep stations. There is a window on either side of the compartment allowing observation of outside. The remaining part of the compartment is packed with equipment and experiments.

The module is connected to the visiting Shenzhou and Tianzhou spacecraft via an androgynous docking mechanism developed by Shanghai Academy of Spaceflight Technology (SAST). The system is believed to have derived from the Russian APAS-75, consisting of a docking port, radio beacons, transponders, communication antenna, UHF radar, laser rangefinder, and electro-optical tracking system. Visiting astronauts enter the Experimental Compartment via the hatch on the 0.8 m-diameter docking port. The docking port on Tiangong 2 has been modified in order to support in-orbit refuelling/resupply operations.

Behind the experiment compartment is a 1.1 m-long transition section, tapered from 3.35 m diameter of the experiment compartment to the 2.25 m diameter of the aft service compartment. The section houses the nitrogen and oxygen tanks used for environmental control, and the water tank. The gases are stored in steel alloy spheres at a pressure of 21 Mpa.

The aft Service Compartment is about 3.3 m in length and 2.5 m in diameter, and has been derived from the Shenzhou service module. The Space Laboratory is fitted with a different propulsion system to that of Shenzhou, with a 490-N dual-chamber high-expansion-ration main engine, four sets of two small aft-firing engines at the base to provide vernier thrust for fine manoeuvres, four sets of two small engines mounted around the external base of the module for pitch/yaw control, and four roll control thrusters. The unified propulsion system feeds both attitude control and main engines from four 230-litre propellant tanks loaded with up to 1,000 kg of N2O4/MMH propellants. The engines are pressure-fed using six 20-litre titanium cold gas tanks pressurised to 23 Mpa. This gas is used to force propellant at 2 Mpa using diaphragms within the propellant tanks.

Systems

Two four-panel solar wings, with a total span of about 23 m, deploy from the sides of the Service Compartment. These can be rotated to obtain maximum solar insolation regardless of spacecraft attitude. Each wing, about 3.1 m x 10 m, provides about double the electrical power of the Shenzhou system (total about 7 kW peak, 2.5 kW average). The back surface filled silicon solar cells of the arrays have an efficiency of 14.8% on Shenzhou. Sun sensors between the panels measure the sunlight incidence angle which allows the panels to be automatically commanded to an optimum angle. Silver-zinc batteries in the service module provide emergency power in case of failure of the solar arrays. The spacecraft’s power bus operates at 28 V.

The module is fitted with a robotic arm, developed by China Aacademy of Space Technology. The 10-m long robotic arm is designed to help the assembly and maintenance of the space station, move equipment and supplies around the station, and support astronauts in EVA.

Onboard Payloads

The Banxing 2 micro satellite, designed by Shanghai Academy of Spaceflight Technology (SAST), will be launched on the piggyback of Tiangong 2 and then released in orbit to demonstrate relevant technologies. Just like its predecessor Banxing 1 launched by the Shenzhou 7 mission in 2008, Banxing 2 will probably also carry an onboard camera to capture images of the mothership in orbit.

Tiangong 2 carries a total of 14 mission and experiment packages, including:

Image Gallery

An orbital view of the Tiangong 2 (right) and Shenzhou 11 (left) complex, captured by the BX-2 CubeSat

Chronology

2011 January – Cargo ship development began. China Academy of Space Technology (CAST) was awarded the development contract. By August 2014, the cargo spacecraft design had been finalised and the spacecraft was officially named Tianzhou (Sky Vessel). The first full-size prototype of the Tianzhou spacecraft was completed in April 2015. Production of the Tianzhou 1 vehicle began in April 2016 and the spacecraft was completed in January 2017.

2011 – Tiangong 2 airframe constructed. The launch of Tiangong 2 came almost exactly five years after the launch of the first Space Laboratory module Tiangong 1 in September 2011, though the airframe of a second module was constructed the same time as Tiangong 1 to serve as a backup. Following the successful launch of Tiangong 1, the backup vehicle was developed into an improved Space Laboratory module for the follow-up missions. To ensure the ‘new’ space module was still qualified for orbital flight, engineers of CAST carefully assessed the conditions of nearly 300 components and parts on the space module, either putting them through a life-extension process or replacing those that no longer met the requirements.

2016 July – Tiangong 2 launch campaign began. The launch campaign began with the arrival of the Tiangong 2 module at the launch centre on 9 July, after a two-day train journey from its fabrication facility at the Beijing Space City where it was stored for the past five years. Two CZ-2F launch vehicles for the Tiangong 2 and Shenzhou 11 missions were delivered to the launch centre by railway in early August. Upon its approval, the Tiangong 2 module was examined and assembled inside the Spacecraft Non-Hazard Operation Building, before being moved to the Spacecraft Hazard Operation Building for the irreversible process of fuelling with liquid propellants and loading of pressurised gases. The completed spacecraft inside its payload fairing was rolled to the Launch Vehicle Vertical Processing Building, where the CZ-2F launch vehicle was assembled. The spacecraft inside the payload fairing was then hoisted onto the top of the launch vehicle for payload integration.

2016 August 13 – Shenzhou 11 launch campaign began. The Shenzhou 11 spacecraft vehicle was transported in special containers by a military cargo plane to the Dingxin Airbase, before making a 76 km journey by road to the launch site. Upon its arrival, the spacecraft was first assembled inside the Spacecraft Non-Hazardous Operation Building in the technique area. It then made a transit to the Spacecraft Hazardous Operation Building for the process of fuelling with liquid propellants and loading of pressurised gases. The assembled and fuelled spacecraft was then integrated with its payload fairing, before moving to the Launch Vehicle Horizontal Processing Building for integration with the launch vehicle and launch escape tower.

2016 September 9 – Tiangong 2 launch countdown. The launch vehicle stack sitting vertically atop the Mobile Launcher Platform (MLP) was rolled out to Pad 921 (SLS1). After the mission control gave a Go for launch, fuelling of the CZ-2F launch vehicle with liquid propellants began in the morning of 14 September.

2016 October 10 – Shenzhou 11 launch countdown. The completed CZ-2F/Shenzhou 11 stack sitting vertically atop the Mobile Launcher Platform (MLP) was rolled out to Pad 921 (SLS1). The prime and backup mission crews took part in an all-system launch rehearsal inside the Shenzhou 11 vehicle on the launch pad on Thursday 13 October. The identity of the two prime crew members, Commander and two-time spaceflight veteran Jing Haipeng and first-timer flight engineer Chen Dong, were only disclosed to public at T minus 22 hours, with a press conference held at 09:00 CST on Sunday 16 October. At the same time as the press conference was underway, the launch vehicle sitting on the launch pad began the irreversible process of fuelling with oxidiser (Dinitrogen Tetroxide, or N2O4) and fuel (Unsymmetrical Dimethylhydrazine, or UDMH).

2016 October 17 – Shenzhou 11 mission. At about 04:30 CST, the two astronauts in their pressure suit attended a simple farewell ceremony and were met by General Fan Changlong, Vice Chairman of the Central Military Commission, inside the Astronaut Apartment at Site 10 (Dongfeng Space City) of the Jiuquan Satellite Launch Centre. Just before 05:00 CST, the two emerged in the courtyard outside the Astronaut Apartment and boarded a minibus for a 15-minute journey to the launch site 6.5 km away. The CZ-2F (Y11) launch vehicle carrying the Shenzhou 11 spacecraft with its two-man crew lifted off from Pad 921 at the Jiuquan Satellite Launch Centre at 07:30:31 CST (23:30:31 UTC on 16 October). Commander Jing Haipeng occupied the central seat in the spacecraft’s re-entry module, and flight engineer Chen Dong was seated on his right.

About 10 minutes after lift-off, the spacecraft was placed into a 197 km x 361 km initial parking orbit. Control of the spacecraft was officially handed over from the Jiuquan Launch Mission Control Centre to the Beijing Aerospace Control Centre (BACC). After five orbital elevation orbital burns in 48 hours, the Shenzhou vehicle elevated to a 393 km orbit. In the previous Shenzhou missions, the rendezvous docking with the target vehicle (space laboratory) was performed on a 343 km orbit. The new flight sequence is a closer imitation of the rendezvous docking operation that will be used by the future manned space station. Shenzhou 11 reached a position about 52 km away from Tiangong 2 in the early morning on 19 October, and the automated rendezvous and docking sequence was initiated. The two vehicles were fully joined at 03:34 CST and the two astronauts entered the Tiangong 2 module shortly after.

Over the next 30 days, the two crew members carried out a total of 14 scientific and engineering experiments. They were also able to watch live TV programmes including news and sport matches. On Day 5 (23 October), at 07:31 CST, the crew released a CubeSat named Banxing 2 (BX-2), which was carried into space by Tiangong 2. On Day 6 (24 October), commander Jing Haipeng celebrated his 50th birthday. On Day 8 (26 October), Jing Haipeng tried a specially-designed suit for cardiovascular research in microgravity environment. In his email correspondence with the public, Jing said that he had adapted to life on orbit, spending on average six hours per day in sleep. The two-man crew of the Shenzhou 11 mission returned to Earth safely in the afternoon of 18 November after a record 32-day spaceflight mission.

2017 February 5 – Tianzhou 1 launch campaign began. The cargo spacecraft left Tianjin for the Wenchang Space Launch Centre aboard a cargo ship. After a week voyage the spacecraft arrived at Wenchang on 13 February for final assembly and testing. On 11 March, the CZ-7 (Y2) launch vehicle also arrived at Wenchang. By 30 March, the various mission payloads had all arrived at the launch centre for testing and loading.

2017 April 17 – Tianzhou 1 launch countdown. The assembled launch vehicle and spacecraft stack rolled out from the Vehicle Assembly Building at the Wenchang Space Launch Centre atop the Mobile Launcher Platform. After 2.5 hours of transit, the giant 1,800-tonne platform carrying the launch vehicle arrived at Pad 201. Fuelling of the kerosene liquid fuel for the two-stage CZ- 7 launch vehicle began at T minus 12 hours in the morning of 20 April, and fuelling of the liquid oxygen began at T minus 8 hours. The fuelling process lasted until about T minus 40 minutes.

2017 April 20 – Tianzhou 1 mission. At 19:41:35 CST (11:41:35 UTC), the CZ-7 (Y2) launch vehicle carrying Tianzhou 1 lifted off from Pad 201 of Wenchang Space Launch Centre. After 10 minutes of flight, the second-stage engine shut down at 19:51:38 CST and the spacecraft was placed into a 200 x 383 km, 42.8° inclination initial parking orbit. Few moments later, the spacecraft’s two solar panel wings were successfully deployed, and the launch mission was declared a success. After entering an initial 200 x 380 km parking orbit, the cargo spacecraft, carrying nearly 6 tonnes of equipment and supplies including 2 tonnes of liquid propellants, performed a number of orbit elevation and refinement burns to meet the Tiangong 2 space laboratory module on a 400 km orbit. Tianzhou 1 then performed an automated rendezvous docking with the unoccupied Tiangong 2 module, and the two vehicle were fully docked at 12:23 CST (04:23 UTC) on 22 April. The first on-orbit refuelling demonstration was completed at 19:07 CST (11:07 UTC) on 27 April. The mission has been hailed by Chinese media as a great accomplishment and major milestone, which marks the successful conclusion of the second phase of China’s human spaceflight programme (Project 921-II) and paves the way for the construction of a permanent space station on in the third and final phase of the programme by 2022. Tianzhou 1 remained docked with Tiangong 2 over the next two months, with a second refuelling demonstration taking place in late June. At 09:47 CST on 21 June, Tianzhou 1 was undocked with the space laboratory module to begin its autonomous flight, during which it would demonstrate sophisticated orbital manoeuvres and carry out scientific experiments with its onboard applications packages. At 15:03 CST on 1 August, Tianzhou 1 released a 3U CubeSat, which was then successfully captured by the ground tracking network.